As portable electronic devices, electronic devices such as video cameras with video tape recorders, portable telephones, lap top computers, or the like have been usually broadly employed. These portable electronic devices have been devised to be compact and light by considering the utility of them. As power sources used for the portable electronic devices which are designed to be compact and light, compact and light secondary batteries having high energy density have been demanded in order not to prevent the electronic devices from being compact land light.
For meeting such a demand, there have been provided nonaqueous electrolyte secondary batteries which employ a graphite material using the intercalation reaction of lithium ions between graphite layers or a carbonaceous material to which doping and dedoping actions of lithium ions to pores as an anode material.
As the performance of the recent portable electronic device has been improved, a demand for the capacity of the secondary battery used for such a electronic device has been more increased. As a secondary battery for meeting such a demand, when light metal such as lithium metal is directly employed as the anode material of the nonaqueous electrolyte secondary battery, the light metal is apt to be deposited in the shape of a dendrite on an anode during a charging process and a current density becomes extremely high at the end of the dendrite. Therefore, a cycle life is disadvantageously decreased due to the decomposition of nonaqueous electrolyte solution or the internal short-circuit of the battery is inconveniently generated due to an excessive growth of the dendrite.
In order to solve such problems, a secondary battery using lithium-lead alloy is proposed as an anode material in Japanese Patent Publication No. hei 3-53743, Japanese Patent Publication No. hei 5-34787, Japanese Patent Publication No. hei 7-73044 and Japanese Patent Publication. No. hei 8-138654. In Japanese Patent Publication No. hei 4-47431 and Japanese Patent Publication No. hei 3-64987, a secondary battery using bismuth-tin-lead-cadmium alloy is proposed. There is a possibility that lead, bismuth and cadmium used therein may degrade a global environment when they are discharged outside.
In Japanese Patent Laid-Open No. hei 7-302588, Japanese Patent Laid-Open No. hei 10-199524, Japanese Patent Laid-Open No. hei 7-326342, Japanese Patent Laid-Open No. hei 10-255768 and Japanese Patent Laid-Open No. hei 10-302770, a secondary battery using a silicon alloy as an anode material is proposed. Although the silicon alloy used in this battery has a very little problem to a global environment, it has some reaction with an organic solvent. Consequently, the silicon alloy is low in its cyclic characteristics with charging and discharging operations repeated as required for the secondary battery, so that it is difficult to put the silicon alloy to practical use.
In Japanese Patent Publication No. hei 4-12586, Japanese Patent Laid-Open No. hei 10-16823 and Japanese Patent Laid-Open No. hei 10-308207, a secondary battery employing an alloy material using tin and nickel is disclosed. The nickel used here is insufficient in view of cyclic characteristics. In Japanese Patent Laid-Open No. sho 61-66369, a secondary battery using lithium, aluminum and tin as an anode material is disclosed. In Japanese Patent Laid-Open No. sho 62-145650, a secondary battery using an alloy of tin and zinc is disclosed. However, both the secondary batteries disclosed in these publications are disadvantageously serious in their cyclic deterioration in accordance with changes of material forms due to the doping and dedoping of Li. In Japanese Patent Laid-Open No. hei 8-273602, a secondary battery using a tin alloy including phosphorus of 1 wt % to 55 wt % as an anode material is disclosed. However, this battery is not satisfactory in its cyclic characteristics. In Japanese Patent Laid-Open No. hei 10-223221, a secondary battery using Cu2NiSn and Mg2Sn as an anode material is disclosed. However, when the influence of Ni metal forming these materials applied to a human body and the scattering of powder in air due to an exothermic reactivity of Mg and oxygen or the like are considered, this battery is hardly used and is poor in its practicability.
In Japanese Patent Laid-Open No. sho 10-308207, a secondary battery using an alloy of tin and copper as an anode material is disclosed. However, this battery shows a discharging capacity of 300 mAh/g for a first cycle, which is lower than that of a currently used carbon material, so that this battery is insufficient to be put to practical use. In Japanese Patent Laid-Open No. hei 11-86854, is disclosed a secondary battery using as anode material a mixture composed of a tin-containing phase which dopes with Li and a phase having Mn, Fe, Co, Ni and Cu which does not dope with Li. Since this battery has the phase which does not dope with Li in the mixture to prevent the movement of Li, its cyclic characteristics are not satisfactory.